I got replies from two. The solution is to upgrade to the latest IPI
controller if the problem occurs again. B.Rea@csc.canterbury.ac.nz had
already posted his summary to this list for a similar problem. Thanks to
those who replied.

We had errors like this after adding an S-bus controller to a recently
upgraded 670MP running SunOS 4.1.2. Occasionally, however, the system
would hang and when re-booted there were problems with the file system
which fsck would not correct. The problem became so severe that we are
not using the IPI disk sub-system. Instead, we had to re-construct our
system on new SCSI disks which were purchased at the same time as the
670 upgrade.

We are waiting a decision from SUN Canada on what our next step will be.